The invention relates to lens array sheets used for stereoscopic photography and stereoscopic printing and picture display apparatuses, more particularly to lens array sheets used in display apparatuses that are demanded to meet the requirements of dimensional accuracy and dimensional stability for image display.
In recent years, it has been known to dispose a lens array sheet including an array of cylindrical lenses (lenticular lenses) is disposed on the front face of a planar display apparatus such as a liquid crystal display panel so that viewers can stereoscopically watch images without wearing any dedicated eye glasses.
The lens array sheet is a light beam control device to be disposed on the front faces of display apparatuses where pixel positions are fixed, for example, liquid crystal display apparatuses for direct viewing or projection, plasma display apparatuses, and organic EL display apparatuses. The light beam control device controls light beams from the display apparatuses to present stereoscopic images in the direction of viewers. There are different types of lens array sheets; glass-made lens array sheets, resin-made lens array sheets, and lens array sheets having a structure where a resin sheet is bonded to a glass base.
FIG. 7 illustrates a glass lens array sheet 100 to be disposed on the front faces of apparatuses that display stereoscopic images. The lens array sheet 100 has a base 101 and a lens array layer 102. The base 101 and the lens array layer 102 are both made of glass and integrally formed. A flat glass is used to form the base 101. The lens array layer 102 has a plurality of glass cylindrical lenses that are adjacently juxtaposed and unidirectionally in parallel with one another.
In the glass lens array sheet 100, the glass base 101 is, for example, processed by press molding and subjected to physical and/or chemical treatments, and the glass lens array layer 102 is directly formed on the resulting glass base 101 without an intermediate base therebetween. In the lens array sheet 100 entirely made of glass, its coefficient of linear thermal expansion is small, and the glass of the lenses and the glass of pixels have an equal coefficient of linear thermal expansion. These factors effectively lessen the variability of a juxtaposition pitch of the cylindrical lenses that may be caused by temperature changes, thereby ensuring that an expected alignment is retained between the juxtaposition pitch of the cylindrical lenses and a pixel pitch (the pixels are arranged on the opposite side of the stereoscopic vision side (viewer's eye position) of the lens array sheet 100). As a result, a level of performance required to stereoscopically display images is reliably maintained over a long period of time. However, a problem of the lens array sheet is a μm-order fine glass processing demanded for the lens array layer, which increases production cost.
FIG. 8 illustrates a resin lens array sheet 200. In the lens array sheet 200, a resin base 201 and a resin lens array layer 202 are integrally formed, or the resin lens array layer 202 is directly formed on the resin base 201. The resin lens array layer 202 has a plurality of cylindrical lenses that are adjacently juxtaposed and unidirectionally in parallel with one another.
The lens array sheet 200 is made of a resin, for example, polymethyl methacrylate, polycarbonate, or polyethylene terephthalate. Unlike any glass lens array sheets, the lens array sheet 200 thus characterized can be inexpensively produced by extrusion molding or injection molding. On the other hand, the resin used to form the lens array sheet 200 is easily deformed by temperature changes. This generates the following problems: dimensional accuracy is lowered, submicron-order molding precision is not obtained in in-plane direction, and film expansion and contraction when bonded to a panel may lead to a poor alignment with high-definition panels and mid-sized to large panels. These problems make it difficult to reliably maintain a level of performance required to stereoscopically display images.
FIG. 9 is a sectional view of a hybrid lens array sheet 300 including a resin and glass as its materials, which was provided to solve the conventional problems. In the lens array sheet 300, a base 301 is made of a glass and a lens array layer 302 is made of a resin, and the glass base 301 and the resin lens array layer 302 are bonded to each other with an adhesive layer 303 interposed therebetween. In this lens array sheet, the lens array layer 302 has cylindrical lens portions 302a and a planar base layer 302b. The planar base layer 302b is left because the resin lens array layer 302 formed by press molding cannot be further thinned, or the planar base layer 302b is formed as a base that serves to retain the cylindrical lens portions 302a. The lens array sheet 100 of FIG. 7 entirely made of glass requires a large production cost although a high level of performance is reliably maintained. The lens array sheet 200 of FIG. 8 entirely made of a resin is inexpensively produced although a high level of performance is difficult to maintain. Unlike these lens array sheets, the lens array sheet 300 illustrated in FIG. 9, which is a resin-glass hybrid sheet, is an inexpensive sheet that reliably demonstrates a high level of performance over a long period of time.
Related art documents are JP Patent Application Publication No. 2009-198830 and JP Patent Application Publication No. 2008-089906.